I propose to analyze the large amount of informational RNA present in the mature oocyte of Xenopus laevis and to define its role in the control of early development and cell differentiation of the embryo. The results will contribute significantly not only to the understanding of reproduction, but also to the understanding of the control mechanisms in eukaryotic cell biology. There exists in Xenopus oocytes a large amount of poly(A)-containing RNA. I plan to measure its lifetime during oogenesis, its relationship to the total informational content of mature oocyte, its role in oocyte protein synthesis, and its function after fertilization. The specificity of these poly(A)-containing RNA molecules for oogenesis and early embryogenesis will be examined by comparing these sequences with mRNA isolated from somatic tissues. Many of these experiments will employ the technique of high Cot (or Rot) RNA- DNA hybridization using radioactive complementary DNA synthesized with reverse transcriptase. In addition, I plan to isolate from immature oocytes the mRNA species for a defined set of proteins, the ribosomal proteins. Furthermore, the localization of the poly(A)-containing RNA will be examined by in situ hybridization as well as by RNA-DNA hybridization with RNA localized from defined regions of the embryo.